/Engine/Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Public/PartyBeaconClient.h
Tell the server about the reservation update request being made
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(Server, Reliable, WithValidation) virtual void ServerUpdateReservationRequest ( const [FString](API\Runtime\Core\Containers\FString) & SessionId, const [FPartyReservation](API\Plugins\OnlineSubsystemUtils\FPartyReservation) & ReservationUpdate )